(1) Field of the Invention
The present invention is directed to sonar systems. In particular, the present invention is directed to a method for embedding information in sonar.
(2) Description of the Prior Art
Undersea acoustic communication, ranging and target detection is made possible by employing active sonar. Sonar waveforms are often characterized by fundamental parameters such as amplitude, frequency and phase. In an undersea acoustic network environment employing multiple nodes, it is not possible to identify the point of origin of a sonar transmission or echo based solely on signal shape. The ability to tie sonar emissions and echoes to their respective sources is a valuable capability for authentication, identification and countermeasures. There is a need to identify sonar echoes based on their points of origin, mission, and platform, to authenticate friendly returns, to institute countermeasures and to perform covert communications. Prior art methods of identifying sonar echoes include traditional watermarking models, but often impinge upon bandwidth and are not effective in a noisy underwater environment. What is needed is a method to authenticate identify and trace sonar transmissions and echoes by embedding transparent, secure and robust digital watermarks in signal space, where the additional information incurs no cost in bandwidth.